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Frame geometry - effects, impressions, rules of thumb?
So, as I've stated many times, I don't have much of a connoisseur
mentality. In particular, I don't seem to perceive the minute differences in riding characteristics that magazine road testers claim to perceive. In fact, I'm pretty sure most road testers would fail any double-blind test of similar bike frames. But at the same time, I'm sure that frame dimensions or geometry do affect riding properties. I've ridden old Schwinn "ten speeds" that were as stable (for no-hands riding) as railroad cars. And many years ago, I rode a brand new low-end Japanese road bike (maybe Fuji?) that a friend bought for his wife. It was so twitchy she couldn't ride it. I'm sure that longer wheelbase means slower response, other things being equal. And of course, on touring bikes, longer chainstays give heel clearance for rear panniers. Cross bikes and crit bikes tend to have higher bottom brackets for obstacle or pedal-to-ground clearance. But what does the group know about the effect of things like front end "trail"? Some people seem to like more, some less. How about top tube length? If a longer top tube is used (maybe to avoid wheel-to-toe overlap) and a shorter stem is used to compensate, how does that affect handling? If trail is held constant, what does a lower steering angle achieve? How about a lower bottom bracket on a touring bike? Does that do anything beyond lowering standover height? Some have claimed low BB adds stability - yet an "ordinary" or tall bike is far easier to balance than a recumbent. Care to discuss? -- - Frank Krygowski |
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#2
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Frame geometry - effects, impressions, rules of thumb?
On Fri, 17 Jun 2016 22:21:39 -0400, Frank Krygowski
wrote: So, as I've stated many times, I don't have much of a connoisseur mentality. In particular, I don't seem to perceive the minute differences in riding characteristics that magazine road testers claim to perceive. In fact, I'm pretty sure most road testers would fail any double-blind test of similar bike frames. But at the same time, I'm sure that frame dimensions or geometry do affect riding properties. I've ridden old Schwinn "ten speeds" that were as stable (for no-hands riding) as railroad cars. And many years ago, I rode a brand new low-end Japanese road bike (maybe Fuji?) that a friend bought for his wife. It was so twitchy she couldn't ride it. I'm sure that longer wheelbase means slower response, other things being equal. And of course, on touring bikes, longer chainstays give heel clearance for rear panniers. Cross bikes and crit bikes tend to have higher bottom brackets for obstacle or pedal-to-ground clearance. But what does the group know about the effect of things like front end "trail"? Some people seem to like more, some less. How about top tube length? If a longer top tube is used (maybe to avoid wheel-to-toe overlap) and a shorter stem is used to compensate, how does that affect handling? If trail is held constant, what does a lower steering angle achieve? How about a lower bottom bracket on a touring bike? Does that do anything beyond lowering standover height? Some have claimed low BB adds stability - yet an "ordinary" or tall bike is far easier to balance than a recumbent. Care to discuss? Well, a longer wheel base, as you say, usually makes for a more stable bike, increasing Trail seems to slow down handling and bottom bracket height also effects handling by effecting the CG. There is a document - "A FRESH LOOK AT STEERING GEOMETRY by Chris Kvale" - which goes into quite a bit of detail. One of the problems is that everything is interrelated. A lower BB height increases stability but may be a determent for track and cross country. A longer top tube and a shorter head tube, to some extent, effect the strength and flexibility of the frame. Trail, while the easiest to change has some unexpected effects. In the study I mention the writer describes a Cinelli track frame with 68mm trail. He described it as: "extraordinarily stable no-hands, but was very heavy feeling in the corners, seeming to require actual physical steering rather than mere leaning. It is important to note that this bike handles perfectly in its event - steady track time trialing, the very long trail making it easy to stay right on the pole line without wandering". Another point. the head tube length is largely determined by the front wheel size, seat tube length, top tube length and slope. A short seat tube with a level top tube, for a rider with long arms, with a 300C wheel, would result in a shorter, then perhaps ideal, head tube. I believe that the rider also enters into the equation as an experienced rider may be quite happy with a faster handling bike than a "newbe" and generally, a stage race bike is more stable then a criterion bike as the "frisky" crit bike is tiring to ride for long periods and I would guess that the TT or Iron Man bike would be similar. I wonder if there has been a comparison of the bikes used in the RAAM. I know that they use aero bars but I also read that they adjust them for comfort rather than minimum wind resistance. -- cheers, John B. |
#3
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Frame geometry - effects, impressions, rules of thumb?
On 18/06/16 04:21, Frank Krygowski wrote:
So, as I've stated many times, I don't have much of a connoisseur mentality. In particular, I don't seem to perceive the minute differences in riding characteristics that magazine road testers claim to perceive. In fact, I'm pretty sure most road testers would fail any double-blind test of similar bike frames. But at the same time, I'm sure that frame dimensions or geometry do affect riding properties. I've ridden old Schwinn "ten speeds" that were as stable (for no-hands riding) as railroad cars. And many years ago, I rode a brand new low-end Japanese road bike (maybe Fuji?) that a friend bought for his wife. It was so twitchy she couldn't ride it. I'm sure that longer wheelbase means slower response, other things being equal. And of course, on touring bikes, longer chainstays give heel clearance for rear panniers. Cross bikes and crit bikes tend to have higher bottom brackets for obstacle or pedal-to-ground clearance. But what does the group know about the effect of things like front end "trail"? Some people seem to like more, some less. How about top tube length? If a longer top tube is used (maybe to avoid wheel-to-toe overlap) and a shorter stem is used to compensate, how does that affect handling? If trail is held constant, what does a lower steering angle achieve? How about a lower bottom bracket on a touring bike? Does that do anything beyond lowering standover height? Some have claimed low BB adds stability - yet an "ordinary" or tall bike is far easier to balance than a recumbent. Care to discuss? This is the best explanation I found; http://www.cyclingabout.com/understa...rame-geometry/ Adding longer stems to short top tubes works, ime, for 5cm or so extensions, after that it feels very odd in the steering department. |
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Frame geometry - effects, impressions, rules of thumb?
On Saturday, June 18, 2016 at 2:05:57 AM UTC-4, Tosspot wrote:
On 18/06/16 04:21, Frank Krygowski wrote: So, as I've stated many times, I don't have much of a connoisseur mentality. In particular, I don't seem to perceive the minute differences in riding characteristics that magazine road testers claim to perceive. In fact, I'm pretty sure most road testers would fail any double-blind test of similar bike frames. But at the same time, I'm sure that frame dimensions or geometry do affect riding properties. I've ridden old Schwinn "ten speeds" that were as stable (for no-hands riding) as railroad cars. And many years ago, I rode a brand new low-end Japanese road bike (maybe Fuji?) that a friend bought for his wife. It was so twitchy she couldn't ride it. I'm sure that longer wheelbase means slower response, other things being equal. And of course, on touring bikes, longer chainstays give heel clearance for rear panniers. Cross bikes and crit bikes tend to have higher bottom brackets for obstacle or pedal-to-ground clearance. But what does the group know about the effect of things like front end "trail"? Some people seem to like more, some less. How about top tube length? If a longer top tube is used (maybe to avoid wheel-to-toe overlap) and a shorter stem is used to compensate, how does that affect handling? If trail is held constant, what does a lower steering angle achieve? How about a lower bottom bracket on a touring bike? Does that do anything beyond lowering standover height? Some have claimed low BB adds stability - yet an "ordinary" or tall bike is far easier to balance than a recumbent. Care to discuss? This is the best explanation I found; http://www.cyclingabout.com/understa...rame-geometry/ Adding longer stems to short top tubes works, ime, for 5cm or so extensions, after that it feels very odd in the steering department. you would 'get over it' as previously noted, muh Raleigh sports tourer...a fine balanced ride... was to nervous for sand skim berms alternating with loose asphalt good asphalt corse sand.... I wuz working too hard on 1 3/8th's 3 rib kendas a donor gave me a same model mixte double tube bike Measuring n eyeballing the woman's fork seemed to say the trail was greater. by an 1/8th" the difference calmed the balanced frame down immediately n off I rode into the sunset happy as a clam |
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